In a metal-oxide-semiconductor field-effect transistor (MOSFET), voltage is applied on the gate to control the current in a channel region to generate a switching signal (on-off). However, when semiconductor technology enters into a sub-45 nm node, the channel current control ability of traditional planar MOSFETs may become weak, thus a severe leakage current may be generated. Fin field-effect transistors (FinFETs) are developed to replace the traditional planar MOSFETs. A FinFET is a multiple-gate device and may include semiconductor fin structures protruding from the surface of a semiconductor substrate, a gate structure covering top and side surfaces of the fin structure, and source/drain regions in the fin structure at both sides of the gate structure.
FIG. 1 illustrates a three dimensional structure of an existing FinFET. The FinFET includes a semiconductor substrate 101; a protruding fin 103 formed by etching a top portion of the semiconductor substrate 101 on the semiconductor substrate 101; a dielectric layer 104 covering the surface of the substrate 101 and a portion of the sidewalls of the fin 103; and a gate structure 105 crossing over the fin 103 and covering a portion of the top and the sidewalls of the fin 103. The gate structure 105 may include a gate dielectric layer (not shown) and a metal gate (not shown) on the gate dielectric layer.
However, during an operation of the FinFET, the bottom of the fin 103 may be relatively far from the gate structure 105, an electric field generated by the gate structure 105 may be relatively weak at the bottom of the fin 103. Thus, the control ability of the gate structure 105 may be relatively weak, a punch-through phenomenon from a source region to a drain region at the bottom of the fin 103 may be generated during the operation of the FinFET. In order to obtain a relatively high carrier mobility, the doping level of the fin 103 of the existing FinFET may be relatively low, the punch-through phenomenon may be more severe, and a short channel effect may become more severe too.
The disclosed device structures, methods and systems are directed to solve one or more problems set forth above and other problems.